The function of osteocalcin, a most abundant non-collagenous protein in bone containing the vitamin K dependent calcium binding amino acid, gamma-carboxyglutamic acid (Gla), is being investigated. Osteocalcin has been isolated and characterized as a 6000 MW protein from many species, however its biosynthetic pathway remains to be elucidated. Studies in bone organ culture and in bone microsome preparations indicate a precursor form of approximately 70,000 MW occurs. This suggests that the vitamin K dependent carboxylation reactions in bone may be analogous to the liver microsomal carboxylation of precursor prothrombin and may regulate conversion of proenzyme to active enzyme forms. The synthesis of osteocalcin in specific bone cell types is being monitored and the effect of bone hormones on osteocalcin synthesis and secretion is being studied. The relation of osteocalcin to the formation of the mineral phase of bone is being examined by measuring its distribution as a function of the density of bone and by comparing the synthesis of the Gla precursor and osteocalcin in normal, vitamin D and vitamin K deficient, 6 week chick bone. Cellular alterations in bone tissue and changes in mineral content are being examined during vitamin K antagonism in chick embryos treated with warfarin. Since calcified cartilage tissues of elasmobranchs are also rich in Gla, vitamin K carboxylated proteins may have a generalized function in calcification and purification of the protein my reveal certain similarities with bone osteocalcin. All pathologically calcified tissues contain Gla residues and the origin of the Gla protein in subcutaneous calcified plaque associated with scleroderma and dermatomysitis is being investigated. To gain further insight into the role of osteocalcin in bone metabolism, the turnover of osteocalcin in patients with bone related disorders is being examined by measuring urine Gla excretion and serum osteocalcin levels. Patients with ectopic calcification disorders excrete 2-3 fold more Gla than controls; rachitic (osteomalacia) children excrete less than their controls.